Method and apparatus for handling RAN assistance information for cell change in wireless communication system

ABSTRACT

A method and apparatus for handling radio access network (RAN) assistance information in a wireless communication system are provided. A user equipment (UE) receives the RAN assistance information with a time value via dedicated signaling from a first cell of a first radio access technology (RAT), and starts a timer with the received timer value. The UE performs a cell change from the first cell of the first RAT to a second cell of a second RAT, and determines whether to stop the timer based on the RAN assistance information. The UE applies the received RAN assistance information while the timer is running. While the timer is running, the UE applies the received RAN assistance information, which is received from the first cell for the first RAT, for RAN-assisted interworking with the second cell of the second RAT.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is the National Phase of PCT International Application No. PCT/KR2015/002225, filed on Mar. 9, 2015, which claims priority under 35 U.S.C. 119(e) to U.S. Provisional Application No. 61/954,570, filed on Mar. 17, 2014 and 61/954,603, filed on Mar. 18, 2014, all of which are hereby expressly incorporated by reference into the present application.

TECHNICAL FIELD

The present invention relates to wireless communications, and more particularly, to a method and apparatus for handling radio access network (RAN) assistance information for cell change in a wireless communication system.

BACKGROUND ART

Universal mobile telecommunications system (UMTS) is a 3rd generation (3G) asynchronous mobile communication system operating in wideband code division multiple access (WCDMA) based on European systems, global system for mobile communications (GSM) and general packet radio services (GPRS). A long-term evolution (LTE) of UMTS is under discussion by the 3rd generation partnership project (3GPP) that standardized UMTS.

The 3GPP LTE is a technology for enabling high-speed packet communications. Many schemes have been proposed for the LTE objective including those that aim to reduce user and provider costs, improve service quality, and expand and improve coverage and system capacity. The 3GPP LTE requires reduced cost per bit, increased service availability, flexible use of a frequency band, a simple structure, an open interface, and adequate power consumption of a terminal as an upper-level requirement.

3GPP/wireless local area network (WLAN) interworking has been discussed. 3GPP/WLAN interworking may be called traffic steering. From rel-8 of 3GPP LTE, access network discovery and selection functions (ANDSF) for detecting and selecting accessible access networks have been standardized while interworking with non-3GPP access (e.g., WLAN) is introduced. The ANDSF may carry detection information of access networks accessible in location of a user equipment (UE) (e.g., WLAN, WiMAX location information, etc), inter-system mobility policies (ISMP) which is able to reflect operator's policies, and inter-system routing policy (ISRP). Based on the information described above, the UE may determine which Internet protocol (IP) traffic is transmitted through which access network. The ISMP may include network selection rules for the UE to select one active access network connection (e.g., WLAN or 3GPP). The ISRP may include network selection rules for the UE to select one or more potential active access network connection (e.g., both WLAN and 3GPP). The ISRP may include multiple access connectivity (MAPCON), IP flow mobility (IFOM) and non-seamless WLAN offloading. Open mobile alliance (OMA) device management (DM) may be used for dynamic provision between the ANDSF and the UE.

The MAPCON is a standardization of a technology which enables configuring and maintaining multiple packet data network (PDN) connectivity simultaneously through 3GPP access and non-3GPP access, and enables a seamless traffic offloading in units of all active PDN connections. For this, an ANDSF server provides access point name (APN) information for performing offloading, routing rule, time of day information, and validity area information, etc.

The IFOM supports mobility in a unit of IP flow, which is more flexible and more segmented than the MAPCON, and seamless offloading. The IFOM enables access to different access networks even when the UE is connected to a PDN using the same APN, which is different from the MAPCON. The IFOM also enables mobility in a unit of specific IP traffic flow, not a unit of PDN, for a unit of mobility or offloading, and accordingly, services may be provided flexibly. For this, an ANDSF server provides IP flow information for performing offloading, routing rule, time of day information, and validity area information, etc.

The non-seamless WLAN offloading is a technology that offloads traffics completely so as not to go through the evolved packet core (EPC) as well as that changes a path of a specific IP traffic to WLAN. The offloaded IP traffic cannot be moved to 3GPP access seamlessly again since anchoring is not performed to the P-GW for mobility support. For this, an ANDSF server provides information as similar as the information provided for the IFOM.

For efficient traffic steering between 3GPP/WLAN, radio access network (RAN) assistance information may be provided by the network. During intra-RAT cell change or inter-RAT cell change, how to handle the RAN assistance information may need to be defined.

SUMMARY OF INVENTION Technical Problem

The present invention provides a method and apparatus for handling radio access network (RAN) assistance information for cell change in a wireless communication system. The present invention provides a method for defining until when dedicated RAN assistance information is applied.

Solution to Problem

In an aspect, a method for handling, by a user equipment (UE), radio access network (RAN) assistance information in a wireless communication system is provided. The method includes receiving, by the UE, the RAN assistance information with a timer value via dedicated signaling, starting, by the UE, a timer with the received timer value, performing, by the UE, cell change, determining, by the UE, whether to stop the timer, applying, by the UE, the received RAN assistance information for RAN-assisted interworking while the timer is running.

In another aspect, a user equipment (UE) configured to handle radio access network (RAN) assistance information in a wireless communication system is provided. The UE includes a radio frequency (RF) unit configured to transmit or receive a radio signal, a processor couple to the RF unit, and configured to receive the RAN assistance information with a timer value via dedicated signaling, start a timer with the received timer value, perform cell change, determine whether to stop the timer, and apply the received RAN assistance information for RAN-assisted interworking while the timer is running.

Advantageous Effects of Invention

Until when dedicated RAN assistance information is applied can be clear.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 shows LTE system architecture.

FIG. 2 shows a block diagram of architecture of a typical E-UTRAN and a typical EPC.

FIG. 3 shows a block diagram of a user plane protocol stack of an LTE system.

FIG. 4 shows a block diagram of a control plane protocol stack of an LTE system.

FIG. 5 shows an example of a physical channel structure.

FIG. 6 shows a graphical representation of Wi-Fi channels in 2.4 GHz band.

FIG. 7 shows an example of a method for handling RAN assistance information according to an embodiment of the present invention.

FIG. 8 shows an example of a method for handling RAN assistance information for inter-RAT cell change according to an embodiment of the present invention.

FIG. 9 shows an example of a method for handling RAN assistance information for intra-RAT cell change according to an embodiment of the present invention.

FIG. 10 shows a wireless communication system to implement an embodiment of the present invention.

MODE FOR THE INVENTION

The technology described below can be used in various wireless communication systems such as code division multiple access (CDMA), frequency division multiple access (FDMA), time division multiple access (TDMA), orthogonal frequency division multiple access (OFDMA), single carrier frequency division multiple access (SC-FDMA), etc. The CDMA can be implemented with a radio technology such as universal terrestrial radio access (UTRA) or CDMA-2000. The TDMA can be implemented with a radio technology such as global system for mobile communications (GSM)/general packet ratio service (GPRS)/enhanced data rate for GSM evolution (EDGE). The OFDMA can be implemented with a radio technology such as institute of electrical and electronics engineers (IEEE) 802.11 (Wi-Fi), IEEE 802.16 (WiMAX), IEEE 802-20, evolved UTRA (E-UTRA), etc. IEEE 802.16m is an evolution of IEEE 802.16e, and provides backward compatibility with an IEEE 802.16-based system. The UTRA is a part of a universal mobile telecommunication system (UMTS). 3rd generation partnership project (3GPP) long term evolution (LTE) is a part of an evolved UMTS (E-UMTS) using the E-UTRA. The 3GPP LTE uses the OFDMA in downlink and uses the SC-FDMA in uplink LTE-advance (LTE-A) is an evolution of the 3GPP LTE.

For clarity, the following description will focus on the LTE-A. However, technical features of the present invention are not limited thereto.

FIG. 1 shows LTE system architecture. The communication network is widely deployed to provide a variety of communication services such as voice over internet protocol (VoIP) through IMS and packet data.

Referring to FIG. 1, the LTE system architecture includes one or more user equipment (UE; 10), an evolved-UMTS terrestrial radio access network (E-UTRAN) and an evolved packet core (EPC). The UE 10 refers to a communication equipment carried by a user. The UE 10 may be fixed or mobile, and may be referred to as another terminology, such as a mobile station (MS), a user terminal (UT), a subscriber station (SS), a wireless device, etc.

The E-UTRAN includes one or more evolved node-B (eNB) 20, and a plurality of UEs may be located in one cell. The eNB 20 provides an end point of a control plane and a user plane to the UE 10. The eNB 20 is generally a fixed station that communicates with the UE 10 and may be referred to as another terminology, such as a base station (BS), an access point, etc. One eNB 20 may be deployed per cell.

Hereinafter, a downlink (DL) denotes communication from the eNB 20 to the UE 10, and an uplink (UL) denotes communication from the UE 10 to the eNB 20. In the DL, a transmitter may be a part of the eNB 20, and a receiver may be a part of the UE 10. In the UL, the transmitter may be a part of the UE 10, and the receiver may be a part of the eNB 20.

The EPC includes a mobility management entity (MME) and a system architecture evolution (SAE) gateway (S-GW). The MME/S-GW 30 may be positioned at the end of the network and connected to an external network. For clarity, MME/S-GW 30 will be referred to herein simply as a “gateway,” but it is understood that this entity includes both the MME and S-GW.

The MME provides various functions including non-access stratum (NAS) signaling to eNBs 20, NAS signaling security, access stratum (AS) security control, inter core network (CN) node signaling for mobility between 3GPP access networks, idle mode UE reachability (including control and execution of paging retransmission), tracking area list management (for UE in idle and active mode), packet data network (PDN) gateway (P-GW) and S-GW selection, MME selection for handovers with MME change, serving GPRS support node (SGSN) selection for handovers to 2G or 3G 3GPP access networks, roaming, authentication, bearer management functions including dedicated bearer establishment, support for public warning system (PWS) (which includes earthquake and tsunami warning system (ETWS) and commercial mobile alert system (CMAS)) message transmission. The S-GW host provides assorted functions including per-user based packet filtering (by e.g., deep packet inspection), lawful interception, UE Internet protocol (IP) address allocation, transport level packet marking in the DL, UL and DL service level charging, gating and rate enforcement, DL rate enforcement based on access point name aggregate maximum bit rate (APN-AMBR).

Interfaces for transmitting user traffic or control traffic may be used. The UE 10 is connected to the eNB 20 via a Uu interface. The eNBs 20 are connected to each other via an X2 interface. Neighboring eNBs may have a meshed network structure that has the X2 interface. A plurality of nodes may be connected between the eNB 20 and the gateway 30 via an S1 interface.

FIG. 2 shows a block diagram of architecture of a typical E-UTRAN and a typical EPC. Referring to FIG. 2, the eNB 20 may perform functions of selection for gateway 30, routing toward the gateway 30 during a radio resource control (RRC) activation, scheduling and transmitting of paging messages, scheduling and transmitting of broadcast channel (BCH) information, dynamic allocation of resources to the UEs 10 in both UL and DL, configuration and provisioning of eNB measurements, radio bearer control, radio admission control (RAC), and connection mobility control in LTE_ACTIVE state. In the EPC, and as noted above, gateway 30 may perform functions of paging origination, LTE_IDLE state management, ciphering of the user plane, SAE bearer control, and ciphering and integrity protection of NAS signaling.

FIG. 3 shows a block diagram of a user plane protocol stack of an LTE system. FIG. 4 shows a block diagram of a control plane protocol stack of an LTE system. Layers of a radio interface protocol between the UE and the E-UTRAN may be classified into a first layer (L1), a second layer (L2), and a third layer (L3) based on the lower three layers of the open system interconnection (OSI) model that is well-known in the communication system.

A physical (PHY) layer belongs to the L1. The PHY layer provides a higher layer with an information transfer service through a physical channel. The PHY layer is connected to a medium access control (MAC) layer, which is a higher layer of the PHY layer, through a transport channel. A physical channel is mapped to the transport channel. Data between the MAC layer and the PHY layer is transferred through the transport channel. Between different PHY layers, i.e., between a PHY layer of a transmission side and a PHY layer of a reception side, data is transferred via the physical channel.

A MAC layer, a radio link control (RLC) layer, and a packet data convergence protocol (PDCP) layer belong to the L2. The MAC layer provides services to the RLC layer, which is a higher layer of the MAC layer, via a logical channel. The MAC layer provides data transfer services on logical channels. The RLC layer supports the transmission of data with reliability. Meanwhile, a function of the RLC layer may be implemented with a functional block inside the MAC layer. In this case, the RLC layer may not exist. The PDCP layer provides a function of header compression function that reduces unnecessary control information such that data being transmitted by employing IP packets, such as IPv4 or Ipv6, can be efficiently transmitted over a radio interface that has a relatively small bandwidth.

A radio resource control (RRC) layer belongs to the L3. The RLC layer is located at the lowest portion of the L3, and is only defined in the control plane. The RRC layer controls logical channels, transport channels, and physical channels in relation to the configuration, reconfiguration, and release of radio bearers (RBs). The RB signifies a service provided the L2 for data transmission between the UE and E-UTRAN.

Referring to FIG. 3, the RLC and MAC layers (terminated in the eNB on the network side) may perform functions such as scheduling, automatic repeat request (ARQ), and hybrid ARQ (HARM). The PDCP layer (terminated in the eNB on the network side) may perform the user plane functions such as header compression, integrity protection, and ciphering.

Referring to FIG. 4, the RLC and MAC layers (terminated in the eNB on the network side) may perform the same functions for the control plane. The RRC layer (terminated in the eNB on the network side) may perform functions such as broadcasting, paging, RRC connection management, RB control, mobility functions, and UE measurement reporting and controlling. The NAS control protocol (terminated in the MME of gateway on the network side) may perform functions such as a SAE bearer management, authentication, LTE_IDLE mobility handling, paging origination in LTE_IDLE, and security control for the signaling between the gateway and UE.

FIG. 5 shows an example of a physical channel structure. A physical channel transfers signaling and data between PHY layer of the UE and eNB with a radio resource. A physical channel consists of a plurality of subframes in time domain and a plurality of subcarriers in frequency domain. One subframe, which is 1 ms, consists of a plurality of symbols in the time domain. Specific symbol(s) of the subframe, such as the first symbol of the subframe, may be used for a physical downlink control channel (PDCCH). The PDCCH carries dynamic allocated resources, such as a physical resource block (PRB) and modulation and coding scheme (MCS).

A DL transport channel includes a broadcast channel (BCH) used for transmitting system information, a paging channel (PCH) used for paging a UE, a downlink shared channel (DL-SCH) used for transmitting user traffic or control signals, a multicast channel (MCH) used for multicast or broadcast service transmission. The DL-SCH supports HARQ, dynamic link adaptation by varying the modulation, coding and transmit power, and both dynamic and semi-static resource allocation. The DL-SCH also may enable broadcast in the entire cell and the use of beamforming.

A UL transport channel includes a random access channel (RACH) normally used for initial access to a cell, a uplink shared channel (UL-SCH) for transmitting user traffic or control signals, etc. The UL-SCH supports HARQ and dynamic link adaptation by varying the transmit power and potentially modulation and coding. The UL-SCH also may enable the use of beamforming.

The logical channels are classified into control channels for transferring control plane information and traffic channels for transferring user plane information, according to a type of transmitted information. That is, a set of logical channel types is defined for different data transfer services offered by the MAC layer.

The control channels are used for transfer of control plane information only. The control channels provided by the MAC layer include a broadcast control channel (BCCH), a paging control channel (PCCH), a common control channel (CCCH), a multicast control channel (MCCH) and a dedicated control channel (DCCH). The BCCH is a downlink channel for broadcasting system control information. The PCCH is a downlink channel that transfers paging information and is used when the network does not know the location cell of a UE. The CCCH is used by UEs having no RRC connection with the network. The MCCH is a point-to-multipoint downlink channel used for transmitting multimedia broadcast multicast services (MBMS) control information from the network to a UE. The DCCH is a point-to-point bi-directional channel used by UEs having an RRC connection that transmits dedicated control information between a UE and the network.

Traffic channels are used for the transfer of user plane information only. The traffic channels provided by the MAC layer include a dedicated traffic channel (DTCH) and a multicast traffic channel (MTCH). The DTCH is a point-to-point channel, dedicated to one UE for the transfer of user information and can exist in both uplink and downlink. The MTCH is a point-to-multipoint downlink channel for transmitting traffic data from the network to the UE.

Uplink connections between logical channels and transport channels include the DCCH that can be mapped to the UL-SCH, the DTCH that can be mapped to the UL-SCH and the CCCH that can be mapped to the UL-SCH. Downlink connections between logical channels and transport channels include the BCCH that can be mapped to the BCH or DL-SCH, the PCCH that can be mapped to the PCH, the DCCH that can be mapped to the DL-SCH, and the DTCH that can be mapped to the DL-SCH, the MCCH that can be mapped to the MCH, and the MTCH that can be mapped to the MCH.

An RRC state indicates whether an RRC layer of the UE is logically connected to an RRC layer of the E-UTRAN. The RRC state may be divided into two different states such as an RRC idle state (RRC_IDLE) and an RRC connected state (RRC_CONNECTED). In RRC_IDLE, the UE may receive broadcasts of system information and paging information while the UE specifies a discontinuous reception (DRX) configured by NAS, and the UE has been allocated an identification (ID) which uniquely identifies the UE in a tracking area and may perform public land mobile network (PLMN) selection and cell re-selection. Also, in RRC_IDLE, no RRC context is stored in the eNB.

In RRC_CONNECTED, the UE has an E-UTRAN RRC connection and a context in the E-UTRAN, such that transmitting and/or receiving data to/from the eNB becomes possible. Also, the UE can report channel quality information and feedback information to the eNB. In RRC_CONNECTED, the E-UTRAN knows the cell to which the UE belongs. Therefore, the network can transmit and/or receive data to/from UE, the network can control mobility (handover and inter-radio access technologies (RAT) cell change order to GSM EDGE radio access network (GERAN) with network assisted cell change (NACC)) of the UE, and the network can perform cell measurements for a neighboring cell.

In RRC_IDLE, the UE specifies the paging DRX cycle. Specifically, the UE monitors a paging signal at a specific paging occasion of every UE specific paging DRX cycle. The paging occasion is a time interval during which a paging signal is transmitted. The UE has its own paging occasion. A paging message is transmitted over all cells belonging to the same tracking area. If the UE moves from one tracking area (TA) to another TA, the UE will send a tracking area update (TAU) message to the network to update its location.

Wi-Fi is a popular technology that allows an electronic device to exchange data wirelessly (using radio waves) over a computer network, including high-speed Internet connections. The Wi-Fi Alliance defines Wi-Fi as any “wireless local area network (WLAN) products that are based on the IEEE 802.11 standards”. However, since most modern WLANs are based on these standards, the term “Wi-Fi” is used in general English as a synonym for “WLAN”.

A device that can use Wi-Fi (such as a personal computer, video-game console, smartphone, tablet, or digital audio player) can connect to a network resource such as the Internet via a wireless network access point. Such an access point (or hotspot) has a range of about 20 meters (65 feet) indoors and a greater range outdoors. Hotspot coverage can comprise an area as small as a single room with walls that block radio waves or as large as many square miles—this is achieved by using multiple overlapping access points.

The 802.11 family consist of a series of half-duplex over-the-air modulation techniques that use the same basic protocol. The most popular are those defined by the 802.11b and 802.11g protocols, which are amendments to the original standard. 802.11-1997 was the first wireless networking standard, but 802.11b was the first widely accepted one, followed by 802.11g and 802.11n. 802.11n is a new multi-streaming modulation technique. Other standards in the family (c-f, h, j) are service amendments and extensions or corrections to the previous specifications.

802.11b and 802.11g use the 2.4 GHz industry-science-medical (ISM) band, operating in the United States under Part 15 of the US Federal Communications Commission (FCC) Rules and Regulations. Because of this choice of frequency band, 802.11b and g equipment may occasionally suffer interference from microwave ovens, cordless telephones and Bluetooth devices. 802.11b and 802.11g control their interference and susceptibility to interference by using direct-sequence spread spectrum (DSSS) and OFDM signaling methods, respectively. 802.11a uses the 5 GHz U-NII band, which, for much of the world, offers at least 23 non-overlapping channels rather than the 2.4 GHz ISM frequency band, where adjacent channels overlap. Better or worse performance with higher or lower frequencies (channels) may be realized, depending on the environment.

The segment of the radio frequency spectrum used by 802.11 varies between countries. In the US, 802.11a and 802.11g devices may be operated without a license, as allowed in Part 15 of the FCC Rules and Regulations. Frequencies used by channels one through six of 802.11b and 802.11g fall within the 2.4 GHz amateur radio band. Licensed amateur radio operators may operate 802.11b/g devices under Part 97 of the FCC Rules and Regulations, allowing increased power output but not commercial content or encryption.

FIG. 6 shows a graphical representation of Wi-Fi channels in 2.4 GHz band. 802.11 divides each of the above-described bands into channels, analogous to the way radio and TV broadcast bands are sub-divided. For example the 2.4000-2.4835 GHz band is divided into 13 channels spaced 5 MHz apart, with channel 1 centered on 2.412 GHz and 13 on 2.472 GHz (to which Japan added a 14^(th) channel 12 MHz above channel 13 which was only allowed for 802.11b). 802.11b was based on DSSS with a total channel width of 22 MHz and did not have steep skirts. Consequently only three channels do not overlap. Even now, many devices are shipped with channels 1, 6 and 11 as preset options even though with the newer 802.11g standard there are four non-overlapping channels—1, 5, 9 and 13. There are now four because the OFDM modulated 802.11g channels are 20 MHz wide.

In addition to specifying the channel centre frequency, 802.11 also specifies a spectral mask defining the permitted power distribution across each channel. The mask requires the signal be attenuated a minimum of 20 dB from its peak amplitude at ±11 MHz from the centre frequency, the point at which a channel is effectively 22 MHz wide. One consequence is that stations can only use every fourth or fifth channel without overlap, typically 1, 6 and 11 in the Americas, and in theory, 1, 5, 9 and 13 in Europe although 1, 6, and 11 is typical there too. Another is that channels 1-13 effectively require the band 2.401-2.483 GHz, the actual allocations being, for example, 2.400-2.4835 GHz in the UK, 2.402-2.4735 GHz in the US, etc.

Since rel-8, 3GPP has standardized access network discovery and selection functions (ANDSF), which is for interworking between 3GPP access network and non-3GPP access network (e.g. WLAN). The ANDSF is elaborated in 3GPP TS 24.312. The ANDSF management object (MO) is used to manage inter-system mobility policy (ISMP) and inter-system routing policy (ISRP) as well as access network discovery information stored in a UE supporting provisioning of such information from an ANDSF. The ANDSF may initiate the provision of information from the ANDSF to the UE. The UE may initiate the provision of all available information from the ANDSF, using a client-initiated session alert message. The relation between ISMP, ISRP and discovery information is that ISMP prioritize the access network when the UE is not capable to connect to the EPC through multiple accesses, ISRP indicate how to distribute traffic among available accesses when the UE is capable to connect to the EPC through multiple accesses (i.e. the UE is configured for IP flow mobility (IFOM), multiple access connectivity (MAPCON), non-seamless WLAN offload or any combination of these capabilities), while discovery information provide further information for the UE to access the access network defined in the ISMP or in the ISRP. The MO defines validity areas, position of the UE and availability of access networks in terms of geographical coordinates. The UE is not required to switch on all UE's supported radios for deducing its location for ANDSF purposes or for evaluating the validity area condition of a policy or discovery information. The UE shall discard any node which is a child of the ANDSF MO root node and is not supported by the UE. The ANDSF server shall discard any node which is a child of the ANDSF MO root node and is not supported by the ANDSF server.

The UE may be provisioned with multiple valid ISMP, ISRP, inter-APN routing policies (IARP) and WLAN selection policies (WLANSP) rules (by the home PLMN (HPLMN) and by the visited PLMN (VPLMN) when it is roaming). The UE does not apply all these valid rules but selects and applies only the “active” rules. Specifically:

-   -   A UE that cannot simultaneously route IP traffic over 3GPP         access and over WLAN access shall select an active ISMP rule, an         active IARP rule and an active WLANSP rule, as specified below.     -   A UE that can simultaneously route IP traffic over 3GPP access         and over WLAN access shall select an active ISRP rule, an active         IARP rule and an active WLANSP rule, as specified below.

When the UE is not roaming, it shall select the active ISMP/ISRP rule, the active IARP rule and the active WLANSP rule to apply from the valid rules provided by the HPLMN based on the individual priorities of these rules (or based on other criteria). For example, the highest priority valid WLANSP rule is selected as the active WLANSP rule.

When the UE is roaming, it may have valid rules from both HPLMN and VPLMN. In this case, the UE shall select the active rules as follows:

1) The active IARP rule is selected from the valid IARP rules provided by the HPLMN.

2) The active ISMP/ISRP rule and the active WLANSP rule are selected based on the UE configuration as follows:

a) The UE is configured to “prefer WLAN selection rules provided by the HPLMN” or not. This configuration can be done either by the user or by the home ANDSF (H-ANDSF) via the list of “VPLMNs with preferred WLAN Selection Rules”. User configuration takes precedence over the H-ANDSF configuration.

b) If the UE is configured not to prefer WLAN selection rules provided by the HPLMN (i.e. the VPLMN to which the UE is registered is included in the list of “VPLMNs with preferred WLAN Selection Rules”), then the UE shall check the WLANSP rule of the VPLMN and shall determine if there are available WLAN access networks that match one or more groups of selection criteria in this rule.

i) If there is at least one WLAN access network that matches one or more groups of selection criteria in the WLANSP rule of the VPLMN, then the UE shall select the active WLANSP rule and the active ISMP/ISRP rule from the valid rules provided by the VPLMN (based on their priority values).

ii) If there is no WLAN access network that matches one or more groups of selection criteria in the WLANSP rule of the VPLMN, then the UE shall select the active WLANSP rule and the active ISMP/ISRP rule from the valid rules provided by the HPLMN. When the UE determines that at least one WLAN access network that matches one or more groups of selection criteria in the WLANSP rule of the VPLMN becomes available, it shall operate as in bullet i) above and may re-select to such WLAN access network.

c) If the UE is configured to prefer WLAN selection rules provided by the HPLMN (i.e. the VPLMN to which the UE is registered is not included in the list of “VPLMNs with preferred WLAN Selection Rules”), then the UE shall check the WLANSP rule of the HPLMN and shall determine if there are available WLAN access networks that match one or more groups of selection criteria in this rule.

i) If there is at least one WLAN access network that matches one or more groups of selection criteria in the WLANSP rule of the HPLMN, then the UE shall select the active WLANSP rule and the active ISMP/ISRP rule from the valid rules provided by the HPLMN (based on their priority values).

ii) If there is no WLAN access network that matches one or more groups of selection criteria in the WLANSP rule of the HPLMN, then the UE shall select the active WLANSP rule and the active ISMP/ISRP rule from the valid rules provided by the VPLMN. When the UE determines that at least one WLAN access network that matches one or more groups of selection criteria in the WLANSP rule of the HPLMN becomes available, it shall operate as in bullet i) above and may re-select to such WLAN access network.

During power-up, while the UE has not registered to any PLMN, the UE shall consider the WLANSP rules provided by the HPLMN as valid and shall select an active WLANSP rule as described above (the one with the highest priority). Thus during power-up the UE can select a WLAN network based on the WLANSP rules provided by HPLMN.

In addition to ANDSF, additional policy may be specified in RAN specification for interworking between 3GPP access network and non-3GPP access network (e.g. WLAN). The additional policy for interworking between 3GPP access network and non-3GPP access network may be referred to as RAN rules. The RAN rule may indicate condition(s) in which the UE is allowed/required to perform traffic steering from 3GPP LTE to WLAN or vice versa. The condition may involve evaluation of measurement results of 3GPP LTE cell, where the measurement result is compared with a relevant RAN rule parameter (i.e., measurement threshold) included in the RAN assistance information. The condition may also involve evaluation of measurement results of WLAN, where the measurement result is compared with a relevant RAN rule parameter (i.e., measurement threshold) indicated by the RAN assistance information.

For ANDSF and RAN rule, the following RAN assistance parameters (or information) may be provided by the RAN and used by the RAN rules and the ANDSF. The RAN assistance information may be provided to the UE via broadcast signaling, i.e. in SystemInformationBlockType17, or via dedicated signaling, i.e. in the RRC-ConnectionReconfiguration message. The RAN assistance information received in SystemInformationBlockType17 is valid only if the UE is camped on a suitable cell. The following RAN assistance parameters provided by the RAN may replace corresponding parameters in ANDSF and RAN rule.

-   -   LTE reference signal received power (RSRP)/UMTS common pilot         channel (CPICH) received signal code power (RSCP) threshold (for         frequency division duplex (FDD))/UMTS primary common control         physical channel (PCCPCH) RSCP threshold (for time division         duplex (TDD))     -   LTE reference signal received quality (RSRQ)/UMTS CPICH Ec/No         threshold (for FDD)     -   WLAN channel utilization in the basic service set (BSS) load IE         (MaximumBSSLoadValue) threshold (the parameter is used 1-way for         determining offload possibility from 3GPP to WLAN or         alternatively hysteresis is used to prevent ping-pong)     -   Available WLAN DL and UL backhaul data rate         (MinBackhaulThreshold) threshold (the parameter is used 1-way         for determining offload possibility from 3GPP to WLAN or         hysteresis is used to prevent ping-pong)

Further, offload preference indicator (OPI) may be provided by the RAN and used by the ANDSF. The OPI value provided by the RAN is compared to a comparison-value provided in the ANDSF policy using an “equal to”-comparison (e.g. OPI_pointer=OPI value) or a “greater/less than”—comparison (e.g. OPI_threshold≥OPI_value) or may be compared to a bitmap (e.g. a set of allowed OPI values) to trigger specific actions, e.g.:

1. OPI may be used in ANDSF to differentiate subscriber subgroups, i.e. gold/silver/bronze. For instance, different subscriber subgroups may have different OPI thresholds/pointers in their ANDSF policies, so that bronze users are offloaded to WLAN first (when cellular load slightly increases) and gold users are kept on LTE till LTE capacity allows so.

2. OPI may be used to differentiate between traffic types, e.g. ANDSF ISRP policies for different IP flows may have different OPI thresholds/pointers so that best effort traffic is offloaded to WLAN first (when cellular load slightly increases).

3. OPI may also be used to trigger specific parts of ANDSF policies and/or ANDSF Mos, OPI may be signaled to the UE in the form of a bitmap which may be compared to a bitmap (e.g. a set of allowed OPI values) stored in the ANDSF to trigger specific parts of ANDSF policies and/or ANDSF Mos. In this case, OPI value may be considered as kind of ANDSF MO index if there are multiple ANDSF Mos.

Examples and clarifications regarding RAN assistance parameters usage in RAN rules and ANDSF are described below. For each parameter “xxx”, there may be two thresholds indicated by the RAN, i.e. “thresXxxLow” for lower threshold, and “thresXxxHigh” for higher threshold.

For 3GPP LTE, the RAN assistance parameters may be used for traffic steering between 3GPP/WLAN as follows. The UE shall move traffic (e.g. for offloadable access point name (APN)) from 3GPP to WLAN if all the following conditions are fulfilled if corresponding parameters are broadcast or send with dedicated signaling:

-   -   Rsrp<threshRsrpLow or Rsrq<threshRsrqLow     -   bssLoad<threshBssLoadLow     -   dlBackhaulRate>threshDlBackhaulRateHigh     -   ulBackhaulRate>threshUlBackhaulRateHigh

The UE shall move offloadable traffic from WLAN to 3GPP if one or more of the following conditions is fulfilled if corresponding parameters are broadcast or send with dedicated signaling:

-   -   Rsrp>threshRsrpHigh     -   Rsrq>threshRsrqHigh

For 3GPP UMTS, the RAN assistance parameters may be used for traffic steering between 3GPP/WLAN as follows. The UE shall move traffic (e.g. for offloadable APN) from 3GPP to WLAN if all the following conditions are fulfilled if corresponding parameters are broadcast or send with dedicated signaling:

-   -   Rscp<threshRscpLow or EcNo<threshEcNoLow     -   bssLoad<threshBssLoadLow     -   dlBackhaulRate>threshDlBackhaulRateHigh     -   ulBackhaulRate>threshUlBackhaulRateHigh

The UE shall move offloadable traffic from WLAN to 3GPP if one or more of the following conditions is fulfilled if corresponding parameters are broadcast or send with dedicated signaling:

-   -   Rscp>threshRscpHigh     -   EcNo>threshEcNoHigh

Currently, a UE in RRC_CONNECTED in 3GPP LTE or CELL DCH (or CELL_FACH) in UMTS may apply RAN assistance information received via dedicated signaling (hereinafter, dedicated RAN assistance information) if such has been received. Otherwise, the UE may apply RAN assistance information received via broadcast signaling (hereinafter, broadcast RAN assistance information). Further, the UE may keep and apply the dedicated RAN assistance information when the UE is in RRC_IDLE in LTE, or CELL_PCH (or URA_PCH) in UMTS, until a time T has passed since the UE has entered RRC_IDLE in 3GPP LTE, or CELL_PCH (or URA_PCH) in UMTS, thereafter the UE may apply the broadcast RAN assistance information. That is, the dedicated RAN assistance information is applied while a timer is running, and upon expiry of the timer, the dedicated RAN assistance information is discarded and the broadcast RAN assistance information is applied. However, upon performing cell change, it is not clear until when the UE should apply the dedicated RAN assistance information while the timer is running.

In order to solve the problem described above, a method for handling RAN assistance information for cell change according to an embodiment of the present invention is described below. Hereinafter, RAN-assisted interworking between 3GPP access network and non-3GPP access network indicates interworking policies (or rules) for access network selection and traffic steering between 3GPP access network and non-3GPP access network based on the assistance information provided by the RAN (e.g. E-UTRAN, UTRAN). RAN rule and ANDSF policy based on the RAN assistance information is an example of the RAN-assisted interworking. It is necessary for the cell to provide the RAN assistance information in order to support RAN-assisted interworking. From the perspective of the UE, the UE may be able to determine whether the cell supports the RAN-assisted interworking by knowing whether the cell provides the RAN assistance information.

FIG. 7 shows an example of a method for handling RAN assistance information according to an embodiment of the present invention.

In step S100, the UE receives the RAN assistance information with a timer value via dedicated signaling. The RAN assistance information received via dedicated signaling may be referred to as dedicated RAN assistance information. The timer may indicate validity of the received dedicated RAN assistance information. Basically, the UE considers that the received dedicated RAN assistance information is valid while the timer is running.

In step S110, the UE starts a timer with the received timer value. The timer may start upon receiving the RAN assistance information or upon RRC connection release after receiving the RAN assistance information.

In step S120, the UE performs cell change. The cell change may be inter-RAT cell change from the first cell of the first RAT to the second cell of the second RAT. The first RAT may be one of 3GPP E-UTRA or UTRA, and the second RAT may be one of UTRA, E-UTRA, GERAN, CDMA high rate packet data (HRPD) or CDMA single-carrier radio transmission technology (1×RTT). Or, the cell change may be intra-RAT (i.e. intra- or inter-frequency in the RAT) cell change.

In step S130, the UE determines whether to stop the timer. For inter-RAT cell change, the UE may determine to stop the timer if the UE is camped on the RAT other than the RAT from which the UE receives the RAN assistance information and/or if the UE cannot read the system information including RAT assistance information (or the indication indicating whether the current cell supports the RAN-assisted interworking). For intra-RAT cell change, the UE may determine to stop the timer if the UE cannot read the system information which indicates whether a cell on which the UE is camped supports the RAN-assisted interworking, or cannot read the system information including RAN assistance information.

In step S140, the UE applies the received dedicated RAN assistance information for the RAN-assisted interworking while the timer is running. While the timer is running, the UE considers that the received dedicated RAN assistance information is valid for RAN rule and/or ANDSF. For inter-RAT cell change, the RAN assistance information may be received from the first cell of the first RAT, and the received RAN assistance information may be applied in the second cell of the second RAT. The received RAN assistance information may be applied while the timer is running only if the UE is in camped normally state. For intra-RAT cell change, the received RAN assistance information may be applied while the timer is running, only if the UE reads the system information and the UE is in camped normally state. Alternatively, the received RAN assistance information may be applied while the timer is running regardless of whether the cell on which the UE is camped supports the RAN-assisted interworking (i.e. whether the cell on which the UE is camped broadcasts the RAN assistance information) or whether the UE is in camped normally state.

FIG. 8 shows an example of a method for handling RAN assistance information for inter-RAT cell change according to an embodiment of the present invention.

In step S200, the UE receives the dedicated RAN assistance information with the timer value from the cell of the first RAT. The timer may indicate the validity of the received dedicated RAN assistance information. The first RAT may be 3GPP LTE.

In step S210, the UE transits from RRC_CONNECTED to RRC_IDLE, and starts the timer with received time value. The timer may start upon receiving the dedicated RAN assistance information. Alternatively, the timer may start upon RRC connection release after receiving the dedicated RAN assistance information. During the timer is running, the UE considers that the received dedicated RAN assistance information is valid (applicable) for interworking policy (e.g. RAN rule, ANDSF).

In step S220, the UE performs inter-RAT cell change (or, inter-RAT cell (re)selection) to the cell of the second RAT. The second RAT may be one of E-UTRA, UTRA, GERAN, CDMA HRPD, CDMA 1×RTT.

In step S230, the UE determines whether to stop/reset or continue the timer. In step S240, the UE applies the received dedicated RAN assistance information in the second cell of the second RAT during the timer is running Upon stopping/resetting the timer, the UE may consider that the received dedicated RAN assistance information is not valid (applicable) for the RAN-assisted interworking and discard the received dedicated RAN assistance information. In other words, only during the timer is running, the UE may consider that the received dedicated RAN assistance information is valid (applicable) for the RAN-assisted interworking rule in the cell of the second RAT.

The UE may determine to stop/reset the timer when at least one of the following conditions is met:

-   -   If the UE is camped on the 3GPP RAT other than the RAT from         which the UE receives the dedicated RAN assistance information:         For example, if the UE receives only the dedicated RAN         assistance information corresponding to 3GPP LTE from 3GPP LTE         network, but does not receive the dedicated RAN assistance         information corresponding to UTMS from UMTS network, and the UE         is camped on UMTS, the UE may stop and reset the timer and does         not apply the received dedicated RAN assistance information. On         the other hand, if the UE receives the dedicated RAN assistance         information corresponding to 3GPP LTE from 3GPP LTE network as         well as the dedicated RAN assistance information corresponding         to UTMS from UMTS network, the UE may not stop the timer and         apply the received dedicated RAN assistance information during         the timer is running, even though the UE reselects the cell from         3GPP LTE to UMTS.     -   If the UE is camped on the 3GPP RAT other than the RAT for which         the UE receives the corresponding dedicated RAN assistance         information: For example, if the UE receives only the dedicated         RAN assistance information corresponding to 3GPP LTE, but does         not receive the dedicated RAN assistance information         corresponding to UTMS, and the UE is camped on UMTS, the UE may         stop and reset the timer and does not apply the received         dedicated RAN assistance information. On the other hand, if the         UE receives the dedicated RAN assistance information         corresponding to 3GPP LTE as well as the dedicated RAN         assistance information corresponding to UTMS, the UE may not         stop the timer and apply the received dedicated RAN assistance         information during the timer is running even if the UE reselects         the cell from 3GPP LTE to UMTS.     -   If the UE cannot read the system information containing RAN         assistance information (or the system information including the         indication which indicates whether the current cell supports the         RAN-assisted interworking rule or not)

Alternatively, when at least one of the conditions described above is met, instead of stopping and resetting the timer and discarding the received dedicated RAN assistance information, the UE may continue the timer and maintain the received dedicated RAN assistance information, but may not apply the received dedicated RAN assistance information. When at least one of the conditions described above is not met any more in a cell, the UE may apply the received dedicated RAN assistance information until the timer expires. Alternatively, the UE may stop the timer and maintain the received dedicated RAN assistance information. When at least one of the conditions described above is not met any more in a cell, the UE may resume the timer and apply the received dedicated RAN assistance information until the timer expires.

Alternatively, the timer may not even be used. In this case, after receiving the dedicated RAN assistance information, when at least one of the conditions described above is met, the UE may consider that the received dedicated RAN assistance information is not valid (applicable) for the RAN-assisted interworking rule and discard the received dedicated RAN assistance information. During the period that at least one of the conditions described above is not met, the UE may consider that the received dedicated RAN assistance information is valid (applicable) for the RAN-assisted interworking until the UE receives the new dedicated RAN assistance information.

Further, only if the UE is in camped normally state in the cell of the second RAT and the timer is running, the UE may apply the received dedicated RAN assistance information. In other words, the UE may not apply the received dedicated RAN assistance information in the cell of the second RAT if the UE is in camped on any cell state even if the timer is running. In this case, if the UE is in camped on any cell state in the cell of the second RAT, the UE may apply only the RAN assistance information broadcast via system information from the currently camped cell. The UE may continue the timer and keep the received dedicated RAN assistance information during the timer is running. If the timer expires, the UE may discard the received dedicated RAN assistance information.

FIG. 9 shows an example of a method for handling RAN assistance information for intra-RAT cell change according to an embodiment of the present invention.

In step S300, the UE receives the dedicated RAN assistance information with the timer value from the cell. The timer may indicate the validity of the received dedicated RAN assistance information.

In step S310, the UE transits from RRC_CONNECTED to RRC_IDLE, and starts the timer with received time value. The timer may start upon receiving the dedicated RAN assistance information. Alternatively, the timer may start upon RRC connection release after receiving the dedicated RAN assistance information. During the timer is running, the UE considers that the received dedicated RAN assistance information is valid (applicable) for the RAN-assisted interworking rule.

In step S320, the UE performs cell change (or, cell (re)selection). In step S330, the UE reads the system information in order to know whether the cell supports the RAN-assisted interworking and determines whether to stop/reset or continue the timer based on the system information. The system information may include RAN assistance information. Alternatively, the system information may include a new indication indicating whether the cell supports the RAN-assisted interworking.

In step S340, only if the cell supports the RAN-assisted interworking, the UE continues the timer. In step S350, the UE applies the received dedicated RAN assistance information during the timer is running That is, if the UE cannot read the system information including RAN assistance information (or the system information including the new indication indicating that the cell provides RAN assistance information), the UE may stop and reset the timer. Only during the timer is running, the UE may consider that the received dedicated RAN assistance information is valid (applicable) for the RAN-assisted interworking.

Alternatively, regardless of the timer, only if the UE reads the system information including RAN assistance information, the UE may apply the received dedicated RAN assistance information during the timer is running. If the UE cannot read the system information including RAN assistance information (or the system information including the above indication), the UE may determine not to apply the received dedicated RAN assistance information (i.e. the UE may discard the received dedicated RAN assistance information) even if the timer is running After determining not to apply the received dedicated RAN assistance information, the UE may stop and reset the timer and may not apply for the RAN-assisted interworking.

Alternatively, regardless of whether the cell supports the RAN-assisted interworking or not, the UE may apply the received dedicated RAN assistance information during the timer is running. In other words, the UE may apply the received dedicated RAN assistance information during the timer is running even if there is no system information including the RAN assistance information (or the new indication).

Alternatively, if the UE cannot read the system information including RAN assistance information (or the new indication), instead of stopping and resetting the timer and discarding the received dedicated RAN assistance information, the UE may stop the timer and maintain the received dedicated RAN assistance information. And, if the UE reads the system information including RAN assistance information (or the system information including the new indication) in the cell, the UE may resume the timer and continue to use the received dedicated RAN assistance information. Alternatively, the UE may continue the timer and maintain the received dedicated RAN assistance information, even if the UE cannot read the system information including RAN assistance information (or the new indication), but may not apply the received dedicated RAN assistance information. And if the UE reads the system information including RAN assistance information (or the new indication) in the cell, the UE may continue to use the received dedicated RAN assistance information until the timer expires.

Alternatively, the timer may not even be used. In this case, after receiving the dedicated RAN assistance information, if the UE cannot read the system information including RAN assistance information (or the new indication), the UE may consider that the received dedicated RAN assistance information is not valid (applicable) for the RAN-assisted interworking and discard the received dedicated RAN assistance information. During the period that the UE reads the system information including RAN assistance information (or the new indication), the UE may consider that the received dedicated RAN assistance information is valid (applicable) for the RAN-assisted interworking until the UE receives the new dedicated RAN assistance information.

Further, only if the UE reads the system information including RAN assistance information (or the new indication) and the UE is in camped normally state, the UE may apply the received dedicated RAN assistance information during the timer is running. In other words, the UE may not apply the received dedicated RAN assistance information if the UE is in camped on any cell state. In this case, if the UE is in camped on any cell state, the UE may apply only the RAN assistance information broadcast via system information from the cell if the cell broadcast the system information including RAN assistance information. The UE may continue the timer and keep the received dedicated RAN assistance information during the timer is running. If the timer expires, the UE may discard the received dedicated RAN assistance information.

Alternatively, the UE may apply the received dedicated RAN assistance information during the timer is running regardless of whether the current camped cell supports the RAN-assisted interworking or not if the UE is in camped normally state. In other words, the UE, which stays in camped normally state, may apply the received dedicated RAN assistance information during the timer is running even if there is no broadcast system information including RAN assistance information (or the new indication).

If a PLMN selection is performed on request by NAS and the registered PLMN (RPLMN) of the UE is different from the PLMN (or equivalent PLMN (EPLMN)) from which the UE receives the dedicated RAN assistance information, the UE may discard the received dedicated RAN assistance information even if the timer is running And if the timer is running, the UE may stop and reset the timer.

FIG. 10 shows a wireless communication system to implement an embodiment of the present invention.

An eNB 800 may include a processor 810, a memory 820 and a radio frequency (RF) unit 830. The processor 810 may be configured to implement proposed functions, procedures and/or methods described in this description. Layers of the radio interface protocol may be implemented in the processor 810. The memory 820 is operatively coupled with the processor 810 and stores a variety of information to operate the processor 810. The RF unit 830 is operatively coupled with the processor 810, and transmits and/or receives a radio signal.

A UE 900 may include a processor 910, a memory 920 and a RF unit 930. The processor 910 may be configured to implement proposed functions, procedures and/or methods described in this description. Layers of the radio interface protocol may be implemented in the processor 910. The memory 920 is operatively coupled with the processor 910 and stores a variety of information to operate the processor 910. The RF unit 930 is operatively coupled with the processor 910, and transmits and/or receives a radio signal.

The processors 810, 910 may include application-specific integrated circuit (ASIC), other chipset, logic circuit and/or data processing device. The memories 820, 920 may include read-only memory (ROM), random access memory (RAM), flash memory, memory card, storage medium and/or other storage device. The RF units 830, 930 may include baseband circuitry to process radio frequency signals. When the embodiments are implemented in software, the techniques described herein can be implemented with modules (e.g., procedures, functions, and so on) that perform the functions described herein. The modules can be stored in memories 820, 920 and executed by processors 810, 910. The memories 820, 920 can be implemented within the processors 810, 910 or external to the processors 810, 910 in which case those can be communicatively coupled to the processors 810, 910 via various means as is known in the art.

In view of the exemplary systems described herein, methodologies that may be implemented in accordance with the disclosed subject matter have been described with reference to several flow diagrams. While for purposed of simplicity, the methodologies are shown and described as a series of steps or blocks, it is to be understood and appreciated that the claimed subject matter is not limited by the order of the steps or blocks, as some steps may occur in different orders or concurrently with other steps from what is depicted and described herein. Moreover, one skilled in the art would understand that the steps illustrated in the flow diagram are not exclusive and other steps may be included or one or more of the steps in the example flow diagram may be deleted without affecting the scope and spirit of the present disclosure. 

The invention claimed is:
 1. A method for handling radio access network (RAN) assistance information in a wireless communication system, the method performed by a user equipment (UE) and comprising: receiving the RAN assistance information with a timer value via dedicated signaling from a first cell of a first radio access technology (RAT); starting a timer with the timer value; performing a cell change from the first cell of the first RAT to a second cell of a second RAT; determining whether to stop the timer based on the RAN assistance information; and applying the RAN assistance information while the timer is running, wherein, while the timer is running, the UE applies the RAN assistance information, which is received from the first cell of the first RAT, for RAN-assisted interworking with the second cell of the second RAT, and wherein when the UE is camped on a RAT other than a RAT from which the UE receives the RAN assistance information, the UE determines to stop the timer.
 2. The method of claim 1, wherein the timer indicates validity of the RAN assistance information.
 3. The method of claim 1, further comprising: performing radio resource control (RRC) connection release after receiving the RAN assistance information, wherein the timer starts upon the RRC connection release.
 4. The method of claim 1, wherein the first RAT is a 3rd generation partnership project (3GPP) universal terrestrial radio access (UTRA) or an evolved UTRA (E-UTRA), and wherein the second RAT is one of the 3GPP UTRA or the E-UTRA, a GSM EDGE radio access network (GERAN), a code division multiple access (CDMA) high rate packet data (HRPD) or a CDMA single-carrier radio transmission technology (1×RTT).
 5. The method of claim 1, wherein the RAN assistance information is applied only if the UE is in camped normally state.
 6. The method of claim 1, further comprising: receiving system information for determining whether a cell, on which the UE is camped, supports the RAN-assisted interworking.
 7. The method of claim 6, wherein the system information includes the RAN assistance information.
 8. The method of claim 6, wherein it is determined to stop the timer if the UE cannot read the system information.
 9. The method of claim 6, wherein the RAN assistance information is applied only if the UE reads the system information and the UE is in camped normally state.
 10. The method of claim 6, wherein the RAN assistance information is applied while the timer is running regardless of whether the cell on which the UE is camped supports the RAN-assisted interworking or whether the UE is in camped normally state.
 11. A user equipment (UE) configured to handle radio access network (RAN) assistance information in a wireless communication system, the UE comprising: a transceiver configured to transmit or receive a radio signal; and a processor coupled to the transceiver, and configured to: control the transceiver to receive the RAN assistance information with a timer value via dedicated signaling from a first cell of a first radio access technology (RAT), start a timer with the timer value, perform a cell change from the first cell of the first RAT to a second cell of a second RAT, determine whether to stop the timer based on the RAN assistance information, and apply the RAN assistance information while the timer is running, wherein, while the timer is running, the UE applies the RAN assistance information, which is received from the first cell of the first RAT, for RAN-assisted interworking with the second cell of the second RAT, and wherein when the UE is camped on a RAT other than a RAT from which the UE receives the RAN assistance information, the UE determines to stop the timer. 